dcb: enforce minimum length on IEEE_APPS attribute

Found by reviewing the warning about unused policy table.
The code implies that it meant to check for size, but since
it unrolled the loop for attribute validation that is never used.
Instead do explicit check for attribute.

Compile tested only. Needs review by original author.
Signed-off-by: Stephen Hemminger <sthemmin@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/dcb/dcbnl.c

@@ -178,10 +178,6 @@ static const struct nla_policy dcbnl_ieee_policy[DCB_ATTR_IEEE_MAX + 1] = {
 	[DCB_ATTR_IEEE_QCN_STATS]   = {.len = sizeof(struct ieee_qcn_stats)},
 };
 
-static const struct nla_policy dcbnl_ieee_app[DCB_ATTR_IEEE_APP_MAX + 1] = {
-	[DCB_ATTR_IEEE_APP]	    = {.len = sizeof(struct dcb_app)},
-};
-
 /* DCB number of traffic classes nested attributes. */
 static const struct nla_policy dcbnl_featcfg_nest[DCB_FEATCFG_ATTR_MAX + 1] = {
 	[DCB_FEATCFG_ATTR_ALL]      = {.type = NLA_FLAG},
@@ -1463,8 +1459,15 @@ static int dcbnl_ieee_set(struct net_device *netdev, struct nlmsghdr *nlh,
 
 		nla_for_each_nested(attr, ieee[DCB_ATTR_IEEE_APP_TABLE], rem) {
 			struct dcb_app *app_data;
+
 			if (nla_type(attr) != DCB_ATTR_IEEE_APP)
 				continue;
+
+			if (nla_len(attr) < sizeof(struct dcb_app)) {
+				err = -ERANGE;
+				goto err;
+			}
+
 			app_data = nla_data(attr);
 			if (ops->ieee_setapp)
 				err = ops->ieee_setapp(netdev, app_data);